1. Field of the Invention
The present invention relates to a claw-pole type stepping motor, and particularly to a structure of a claw-pole type stepping motor, which enables reduction in radial dimension and improvement in performance characteristic.
2. Description of the Related Art
Due to increasing demand for miniaturization of various electronics devices, motors used in the electronics devices are also requested to be downsized increasingly. In a conventional claw-pole type stepping motor of inner rotor structure, magnetic coils of A phase and B phase are typically disposed so as to circumferentially surround a rotor. In such a claw-pole type stepping motor, the outer diameter of a rotor magnet is restricted by the inner diameter of a stator. Accordingly, a rotor magnet in a motor with a small radial dimension is forced to be small in diameter, and therefore the motor characteristic is inevitably degraded significantly. In such a case, a brushless DC motor provided with an encoder as a position detector must be used for position control in place of a claw-pole type stepping motor, and this invites cost increase.
In order to overcome the difficulties described above, Japanese Patent Application Laid-Open No. 2003-009499 teaches a structure of a claw-pole type stepping motor, in which magnetic coils are isolated from each other and disposed respectively toward the both axial end faces of a rotor so as to axially sandwich the rotor. With such a structure, a claw-pole type stepping motor having a diameter of about 6.0 mm or less can be produced with a practical performance characteristic maintained. Such a small motor, however, is very difficult and troublesome to assemble just because of its reduced radial dimension and resultantly increased axial dimension, especially when a large number of components are used.